Conventionally, laser machining systems are used for the cutting, drilling, surface machining and marking of steel, nonferrous materials, ceramics, glass, plastic, leather, cloth, wood or various other materials (hereinafter referred to as the “workpiece”) as well as for the welding of steel, nonferrous and other materials (hereinafter collectively referred to as “machining”). Furthermore, the mainstream types of lasers used include YAG lasers, CO2 lasers and excimer lasers.
For example, a YAG laser machining system may have a constitution wherein laser light generated by a laser oscillator is transmitted through an optical fiber, and concentrated onto the workpiece by means of a condensing lens provided within the head. Moreover, such a head can be manipulated in three dimensions according to an operating procedure stored in a computer or the like, thus permitting extremely fine machining to be performed. Note that protective glass that protects the condensing lens from spatter, fumes, dust and the like (hereinafter referred to as simply “dust”) arising during the machining of the workpiece is provided in the space between the condensing lens and the workpiece. In addition, shield gases, assist gases and other process gases (hereinafter referred to as simply “process gases”) are supplied to the machining area, thus preventing deterioration of the machining quality.
However, in the laser machining as described above, dust arising during machining may adhere to the protective glass and the like, thus preventing the condensing of laser light and causing deterioration in machining quality. To solve this problem, the publication of unexamined Japanese patent application (Kokai) No. JP-A H11-239889 proposes a constitution that comprises a nozzle through which laser light (referred to as a “laser beam” in the publication) and process gases may pass. The constitution further comprises a plurality of ring-shaped flow-straightening plates provided in front of the condensing lens inside a nozzle holding space such that their inside diameter becomes smaller the closer they are to the workpiece. Gases injected from the gas injection nozzle along the flow-straightening plates can be exhausted from internal spaces in the nozzle holder to external spaces. By adopting such a constitution, it is possible to completely block dust during machining and protect the condensing lens, and thus prevent fouling of the window.
In addition, JP-A H05-256947 proposes an internal contamination detection technique for distance measuring apparatus based on optical means. This technique is one whereby fouling of the lens or front glass or the like is detected by catching part of the light used for measuring distances which is scattered backward at the time that the light passes through the lens or front glass or the like.
However, the apparatus proposed in JP-A H11-239889 does not take into consideration the suction of air from the side opposite the gas injection nozzle. Accordingly, when the amount of gas ejected from the gas injection nozzle becomes large, then negative pressure is generated in the vicinity of the gas ejection nozzle, thus drawing in dust in the vicinity and giving rise to turbulent flow also in the interior of the holder, so the ability to exhaust dust is decreased and the ability to prevent the adhesion of dust is also decreased. In addition, while a plurality of ring-shaped flow-straightening plates is provided in order to straighten the flow of gas ejected from the gas injection nozzle and block dust, if the amount of gas ejected from the gas injection nozzle becomes large, then the atmospheric gas in the machining area will also be simultaneously drawn in. Accordingly, the normal machining atmosphere cannot be maintained and the meritorious effect of the flow-straightening plates is diminished and machining quality deteriorates.
In addition, the apparatus proposed in JP-A H05-256947 uses a special optical lens in order to catch the light scattered by fouling, so the head becomes large, thereby adding limitations to the machining orientations and otherwise reducing its degrees of freedom. In addition, in the case that this technique is adopted in a laser machining system, the machining laser is high-powered in contrast to one used for measuring distances, so quartz glass is used for the condensing lens and the fabrication of a special lens using this quartz glass is difficult. Moreover, while the measurement of distance is performed by catching reflected light from the light given off, the intensity of light from outside the apparatus is also caught at the same time. Accordingly, regardless of any fouling of the lens, front glass or the like, the intensity of light caught may also vary depending on the season, weather, time of day or other circumstances at the time of measurement, thereby giving rise to dispersion in the detection data and poor reliability.
The present invention came about in order to solve the aforementioned problems and has as its object to provide a method and apparatus for preventing the fouling of optical components by the adhesion of dust arising during laser machining, by inducting air from the rear of the injection area while injecting gas in the direction in which the laser light passes, so as not to disturb the machining gas, in the space between the workpiece and the head that concentrates laser light from the light source and irradiates the workpiece.